The relationship between charge change and change in electrophoretic mobility will be investigated experimentally for 10 or more protein producing loci that are known to be polymorphic and for at least 5 known monomorphic loci in Drosophila pseudoobscura. The method of investigation will involve primarily the comparison of electrophoretic alleles by Ferguson plot analysis as described by Cobbs and Prakash (1977). The resulting information will indicate the sensitivity of the method of gel electrophoresis in terms of detecting amino acid differences between proteins produced by the loci being studied. The information acquired in this study will also be used to test goodness-of-fit of the patterns of protein polymorphism to the predictions of the step model of Ohta and Kimura (1973).